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TG-S51T resembles TG-S50 in terms of applications
of mild steel, 490 MPa high tensile strength steel,
and Al-killed steel for low temperature services but
is superior in tensile strength under extended
postweld heat treatment conditions.
Fundamental properties
TG-S51T is classified as ER70S-6 in accordance
with AWS A5.18 (Specification for Carbon Steel
Electrodes and Rods for Gas Shielded Arc Welding).
The typical chemical composition of the wire
and the typical mechanical properties of the weld
metal are shown in Table 1 with the AWS requirements.
The gas tungsten arc welding (GTAW) process
may partly be used (e.g. for root pass welding) on
thick-wall work such as pressure vessels and process
pipes that are subject to postweld heat treatment
(PWHT), although the major part of the
welding joints in such equipment are welded generally
by more efficient processes such as shielded
metal arc welding (SMAW), submerged arc welding
(SAW), and gas metal arc welding (GMAW).
In addition, the pipe-to-nozzle joints on a thick,
large pressure vessel may be welded by a mechanized
GTAW for better quality and efficiency. In
these cases, the PWHT may have to be conducted
for long hours according to the thickness of the
work: e.g. 4 hours for 100-mm thick work. When
the work is too big to conduct PWHT at one time
in a particular furnace, the PWHT should necessarily
be conducted several times — thus the total
PWHT hours for some weld joints may be 8 to 16
depending on the number of PWHT times. This is
why the GTAW weld metal may also be required
to satisfy the mechanical properties after long-hour
PWHT.
Table 2 shows the typical mechanical properties of
TG-S51T weld metal after long-hour PWHT. Figure
1 illustrates the effects of PWHT temper
parameter on 0.2% offset strength and tensile
strength. Clearly, TG-S51T weld metal can satisfy
490 MPa under an extended PWHT condition.
Table 1 Typical chemical and mechanical properties of TG-
S51T in comparison with the AWS requirements*1
Filler wire
TG-S51T
AWS A5.18-2005
ER70S-6
C% 0.10 0.06-0.15
Si% 0.89 0.80-1.15
Mn% 1.56 1.40-1.85
P% 0.010 0.025 max.
S% 0.011 0.035 max.
Cu% 0.23 0.50 max.
0.2% OS (MPa) 510 400 min.
TS (MPa) 610 480 min.
El (%) 32 22 min.
IV (J) –29°C: 210 27 min.
1. Chemical compositions are for solid wire, and mechanical properties
are for weld metal in the as-welded condition. Other chemical
elements are specified — Ni, Cr, Mo: 0.15% max. each; V: 0.03%
max. Cu% includes that of Cu-coating.
Suitable for extended PWHT applications
Table 2: Typical mechanical properties of TG-S51T weld
metal after long-hour PWHT
PWHT
(°C × h)
0.2% OS
(MPa)
TS
(MPa)
El
(%)
IV (J)
at –30°C
625 × 8 440 560 34 170
625 × 24 420 550 35 160
Figure 1: Tensile strength and 0.2% offset strength of TG-
S51T weld metal as a function of temper parameter (T: PWHT
temperature by Kelvin; t: PWHT hours).
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